My stomach has a dull burn on the lower left side and my stool is dark.it's been going on about 5 days.

Find out why (below): The dark stool may be due to bleeding. Get a test for occult blood at your pharmacy and check. If the pharmacy doesn't have it, your physician does. If it is positive, the problem is urgent, whether it is am ulcer or another GI problem. If it is negative, you still need to have it evaluated by your doctor. Take Prilosec or a similar medicine meanwhile. No coffee, alcohol or aspirin.